California Reservoirs are now dangerously full

Oroville dam over the weekend releasing water from it's man made spillway AND it's emergency spillway... or basically the hillside in the background of the photo. Picture courtesy of the California Department of Water Resources

Combined liquid precipitation totals for the San Joaquin Valley rain gauges. Since rain amounts can vary drastically in California because of location & elevation, gauges in the valley are combined to help officials better understand potential runoff

Main reservoirs current water levels when compared to the capacity as well as the normal level for this point in the year. Plain to see that several are near capacity and nearly all of them are well above average for this point in the year.

KMSP - Just 18 months after many California lakes were nearly dried up, the state now has too much of a good thing. California has now seen more moisture in the last 8 weeks than it typically does in an entire year. Parts of the Sierra Mountain range have received more than 400” of snow already this season with some coastal and foothills locations pulling in over 2 feet of rain… and their typical wet season has nearly 2 months to go. San Francisco, Sacramento, Los Angeles, and several other cities have recorded one of their wettest Januarys on record and an incredibly wet 8 weeks overall. Thankfully, the moisture has stopped for now but the damage has been done.

One of the state’s biggest reservoirs is now at capacity… and still rising. The California Department of Water Resources (CDWR) installed a spillway into the dammed lake to drain excess water when the lake gets full, but it has been damaged by recent rains. Now the state is scrambling to try and figure out how to avert disaster, which would push the lake to “overtop” the dam and potential bust through the dam itself, sending torrents of water downstream and threaten tens of thousands of people. Not to mention, it would destroy one of the state’s main sources of drinking water. Oroville and the Shasta reservoir are the 2 main sources of drinking water for much of California, all the way down to L.A. The CDWR says there is absolutely no threat of an overtopping happening right now and they are taking steps to make sure that does not happen.

The good news for the area is that there is a backup “emergency spillway” when the lake reaches capacity, as it already has. It’s effectively a slope of land where the water just overtops and spills into the creek below… think of it like filling a bathtub… once you reach the top of the open side, water starts to cascade out. But this emergency spillway has never been used before in the dams 50+ year history, and is not a long term solution. The torrent of water flowing down the hillside can quickly erode hundreds of metric tons of dirt and threaten the dam and the lake itself over time.

Oroville dam is one of several reservoirs at or near capacity, with the largest, Lake Shasta, at one of its highest levels in decades. While California has been in this situation before, it’s been 20 years since many waterways have been this full. It’s also one of the earliest points in the season that reservoirs have filled up. Lake levels don’t typically peak or come close to filling up until late May or early June when runoff from the Sierra’s snowmelt begins winding down and the dry season takes hold. That’s still over 3 months away!

As for Oroville dam, engineers have already estimated the cost to fix the long concrete spillway at over 200 million dollars, but can’t begin repairs until lake levels come down and the spillways stop flowing. This is the unfortunate side effect of finally escaping the drought. Looks like it’s going to be a nerve racking few months for Californians.